Development of a novel optoacoustic imaging system for detection of early breast cancer is the main goal of the parent NIH grant. Comprehensive tests in phantoms resembling properties of the breast with tumors, extensive studies in mastectomy specimen surgically excised from the breast cancer patients and pilot clinical studies on breast cancer patients performed with laser optoacoustic imaging system (LOIS) developed at UTMB demonstrated high sensitivity of the system based on exceptional optical contrast between tumors and normal breast tissues combined with ultrawide-band detection of ultrasonic profiles induced by laser pulses in tumors. The resolution of LOIS matches the resolution of the state-of-the-art ultrasound systems (approximately 1-mm). Presently, two-dimensional optoacoustic images of the breast segments are being acquired with a system with optical fibers delivering laser pulses to one surface of the breast and an arc-shaped array of acoustic transducers receiving signals on the opposite surface of the breast (i.e. optoacoustic detection in so-called forward mode). The experience acquired with LOIS in the course of our project supported by NCI resulted in new ideas on the system modification in order to improve convenience for both, the operator and the patient. In particular, we propose a modification of LOIS to incorporate fiberoptic light delivery system and ultrasonic detectors in one compact hand-piece, with electronics allowing acquisition of breast images in real time and in a fusion similar to ultrasound imaging. Such a novel optoacoustic transducer (OAT) will operate in so-called backward detection mode. In order to perform feasibility studies of the LOIS in backward mode, we propose to enhance infrastructure at Moscow State University (MSU) enabling our collaborators to effectively participate in joint research and development projects on optoacoustic tomography, thereby enhancing the research of US Investigator. MSU group possesses a strong expertise in optoacoustics, nonlinear and ultrawide-band ultrasonics, and laser optics. Such a unique expertise will be very useful for expansion of the scope of the parent NIH grant. Specifically, the goals of the MSU group will be as follows: (1) to perform basic modeling and experimental studies of the optoacoustic tomography in backward mode using a single-element optoacoustic transducer, (2) design, fabricate and test in breast phantoms a hand-held optoacoustic transducer array with multiple optical fibers for illumination and multiple piezoelectric transducers for detection of ultrasonic waves at one and the same site on tissue surface. This project requires funding for equipment and supplies necessary for the MSU group to undertake proposed experiments. Joint feasibility studies in breast phantoms will be carried out at UTMB employing multi-element OAT to be developed at MSU and a multi-channel electronic data acquisition system developed at UTMB.